The speed difference between XEmacs and GNU Emacs is amazing, in that
GNU Emacs is significantly faster, at least for "heavy" usage such as
Gnus. Entering a large summary buffer takes time proportional to the
*square* of the number of messages in the folder. (This is not a wild
guess, a friend has actually measured.) Time to enter a folder of
more than 3000 articles quickly degrades to minutes.
For the longest time I believed this to be a result of XEmacs's
implementation of text properties on top of extents. I planned to
convert Gnus to use extents natively, in the hope that it would speed
up summary buffer generation. But according to profiling, most of the
time is spent in `insert', at least once you discount excessive GC by
increasing gc-cons-theshold. I'm not sure what XEmacs is doing wrong
here. I suspect Mule is to blame, but I can't prove it.
Using FSF Emacs gave me an order-of-magnitude speedup when entering
large newsgroups and large mailing list folders. It's uncanny.